4 Answers
4

Usually when you see a chord, the lowest note played is the root note of the chord. So when you normally see a chord marked as Cm that means play a C minor chord with the lowest note (the bass note) as the root -- C: C, E♭, G.

Normally you play the chord going up. So in the Cm example, you play the rootC, the thirdE♭, and the fifthG:

Musicians like playing around with something called "inversions" of a chord, where you change the ordering of the notes. Normally first inversion is where the second note (which in our example is the third degree of the scale) is played first: E♭, G, C. The C is played higher on the instrument than before:

In the same way, we have second inversion, which is where the fifth degree of the scale is played first:

So what the others were saying follows this logic. You should probably play an Em with the lowest note being a D for the Em(on D) [Em/D]. This can be done in many ways!

Don't let the term "slash notation" bother you. It's simply a chord that has a bass note(the lowest note) that is not normally part of the chord. You find a lot of these chords in songs by The Beatles for instance.

While you are learning and so new at guitar, I suggest using songbooks that have chord diagrams each time you need to play the chord. In time, you won't need any help remembering the chords.

You're speaking to me like I have a clue what I'm doing :) I just recently took up playing guitar. Although maybe it would be better to open up a separate question where this slash notation can be described in more detail and link to that from here so it can hopefully be found easier by searching.
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SamJul 9 '12 at 13:56

To be fair, you asked the original question like you had a clue what you were doing! The other answers have elaborated fully.
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NReilingh♦Jul 10 '12 at 3:38